1. Field of the Invention
The present invention relates to a swash plate type hydraulic drive transmission and a hydrostatic type continuously variable transmission. In particular, the present invention relates to an improvement of a swash plate type hydraulic drive transmission and a hydrostatic type continuously variable transmission each having distributing valves so that when plungers are moved to a side for expanding oil chambers, the oil chambers are communicated to low pressure oil passages; and when plungers are moved to a side for reducing the oil chambers, the oil chambers are communicated to high pressure oil passages.
2. Description of Background Art
A swash plate type hydraulic drive transmission and a hydrostatic type continuously variable transmission is known as disclosed in Japanese Published Unexamined Patent Application No. Hei 11-82288. In this publication, a plurality of first distributing valves are slidably fitted in cylinder blocks in parallel with a plurality of pump plungers that are reciprocatively driven by a first valve swash plate, and a plurality of second distributing valves slidably fitted in cylinder blocks in parallel with a plurality of motor plungers that are reciprocatively driven by a second valve swash plate.
In the prior art, in addition to a plurality of pump cylinder holes and motor cylinder holes, a plurality of sliding holes for slidably fitting therein a plurality of first and second distributing valves are provided in the cylinder block. The diameter of the cylinder block is increased to provide a space for arranging these sliding holes and the number of processes must be increased in order to drill the sliding holes. The first and second distributing valves and a first and a second valve swash plate for driving these distributing valves are necessary and the number of parts is increased.
The present invention has been made in view of such circumstances and an object of the present invention is to provide a swash plate type hydraulic drive transmission and a hydrostatic type continuously variable transmission each having distributing valves which can make a cylinder block smaller thus reducing the number of processes and the number of parts.
To achieve the foregoing object, in the present invention, a swash plate type hydraulic drive transmission includes rotors that are supported in a casing so as to be rotatable about the axis of corresponding cylinder blocks. Plungers are provided with an outer end that is brought into contact with and engaged with swash plates to form oil chambers between the plungers and the closed ends of cylinder holes. The plungers are slidably fitted in a plurality of the bottomed cylinder holes provided in the cylinder blocks in an annular arrangement. Distributing valves allow the oil chambers of the plungers moving to a side for expanding the oil chambers to be in communication with low pressure oil passages and which allow the oil chambers of the plungers moving to a side for reducing the oil chambers to be in communication with high pressure oil passages that are provided to correspond to the plungers between the low pressure oil passages and the high pressure oil passages provided in the rotors and the oil chambers. The distributing valves alternately switch, corresponding to the axial reciprocating motion of the plungers, communication and cutoff communication between a plurality of communication passages communicating with the oil chambers opening to the inner surface of the cylinder holes and a plurality of low pressure and high pressure ports respectively communicating with the low pressure oil passages. The high pressure oil passages open to the inner surface of the cylinder holes.
In the construction of the present invention, distributing valves are constructed so as to switch, by reciprocatively operated plungers, communication and cutoff communication between passages in communication with oil chambers and low pressure and high pressure ports respectively communicating with low pressure oil passages and high pressure oil passages. Sliding holes only for the distributing valves need not be provided in the cylinder block to make the cylinder block smaller and to reduce the number of processes. The number of parts only for the distributing valves are unnecessary to thus reduce the number of parts.
According to the present invention, a hydrostatic type continuously variable transmission in which rotors positioned within cylinder blocks in common with hydraulic pumps and hydraulic motors are supported in a casing so as to be rotatable about the axis of the cylinder blocks. A plurality of pump plungers are provided in the hydraulic pumps to form pump oil chambers between the pump plungers and the closed end of pump cylinder holes and are slidably fitted in the bottomed cylinder holes provided in the cylinder blocks in an annular arrangement. A plurality of motor plungers are provided in the hydraulic motors to form motor oil chambers between the motor plungers and the closed end of the motor cylinder holes that are slidably fitted in the bottomed motor cylinder holes provided in the cylinder blocks in an annular arrangement. A plurality of first distributing valves allow the pump oil chambers of the pump plungers in a suction region to be in communication with low pressure oil passages and which allow the pump oil chambers of the pump plungers in a discharge region to be in communication with high pressure oil passages that are provided and correspond to the pump plungers between the low pressure oil passages and the high pressure oil passages provided in the rotors and the pump oil chambers. A plurality of second distributing valves allow the motor oil chambers of the motor plungers in an expansion region to be in communication with the high pressure oil passages and which allow the motor oil chambers of the motor plungers in a reduction region to be in communication with the low pressure oil passages that are provided and correspond to the motor plungers between the low pressure oil passages and the high pressure oil passages and the motor oil chambers. The first distributing valves alternately switch, corresponding to the axial reciprocating motion of the pump plungers, communication and cutoff communication between a plurality of pump side communication passages in communication with the pump oil chambers opening to the inner surface of the pump cylinder holes and a plurality of first low pressure and high pressure ports respectively in communication with the low pressure oil passages and the high pressure oil passages opening to the inner surface of the pump cylinder holes. The second distributing valves alternately switch, corresponding to the axial reciprocating motion of the motor plungers, communication and cutoff communication between a plurality of motor side communication passages in communication with the motor oil chambers opening to the inner surface of the motor cylinder holes and a plurality of second low pressure and high pressure ports respectively in communication with the low pressure oil passages and the high pressure oil passages opening to the inner surface of the motor cylinder holes.
In the construction of the present invention, first distributing valves are constructed so as to switch, by reciprocatively operated pump plungers, communication and cutoff communication between pump side communication passages in communication with pump oil chambers and first low pressure and high pressure ports respectively in communication with low pressure oil passages and high pressure oil passages. Second distributing valves are constructed so as to switch, by reciprocatively operated motor plungers, communication and cutoff communication between motor side communication passages in communication with motor oil chambers and second low pressure and high pressure ports respectively in communication with low pressure oil passages and high pressure oil passages. Sliding holes only for the first and second distributing valves need not be provided in the cylinder block thus making the cylinder block smaller and reducing the number of processes. In addition, parts only for the first and second distributing valves are unnecessary thus reducing the number of parts.
According to the present invention, the rotor includes the cylinder block and a rotation axis coaxially pressed into the cylinder block, a plurality of the pump side communication passages are in part constructed by a plurality of pump side communication grooves provided in the outer circumferential surface of the rotation axis. A plurality of the motor side communication passages are in part constructed by a plurality of motor side communication grooves provided in the outer circumferential surface of the rotation axis. According to such a construction, the pump side communication grooves and the motor side communication grooves are easily provided in the outer circumferential surface of the rotation axis. Thus, the number of processes can be further reduced.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.